It doesn't seem to exactly parallel the war of the roses, but there's plenty of similarities that got combined to make the plot of FFT.

For one, it is a case of the question of ascencion. Also, alot of what happened in the war of the roses resulted as a consequence of the 100 years war with France, I'm guessing the reference for the 50 years war. There was one point where an infant king was placed on the throne (like Orinas). He grew up to be a weak king, and was also considered sickly, like Orinas' father. Orinas' grandfather was known as a hero in the 50 years war, as the infant-king's dad was in the 100s. The same guy grew up to have a controlling queen, as the queen in FFT was considered to be.

One of the major aspects is that there were many unemployed and disenfranchised soldiers from the 100 years war. The entire citizenry as a whole really suffered from it, too.

There was also a plague in FFT, as the black plague was around at the time, too, and the Templar Knights had a church and headquarters in London, I'm guessing the inspiration for the Temple Knights in Tactics. I don't know if they had a role in the war or if they were even around then.